The aim of the proposed research is to develop a quantitative model to account for visual discrimination functions in which wavelength is a significant variable. The functions (and hence the model) are largely restricted to foveally viewed aperture colors. The model uses as input the spectral sensitivities of the cone pigments. It is widely accepted that these cone spectral sensitivities are transformed into a set of sum and difference signals within the retina and transmitted to higher centers. The goal of the research is to work out the details of this transformation. The transformation equations are based on the results of psychophysical experiments with human observers. However, certain concepts in the theory are taken from electrophysiological experiments, and a serious attempt is made to incorporate the results of such experiments, with the aim of producing a more general model. The significance of the research is that, to the extent that it is successful, it contributes to the solution of the problem of how the visual system transmits information about color.